Digital versatile discs (DVDs) are information storage devices used for storing prerecorded audio information, movies and computer software. The storage mechanism used in DVDs closely resembles that used in compact discs (CDs). DVD players also use the same laser technology as CD players. Briefly, both DVDs and CDs store information as a pattern of pits formed in a metallic substrate. The pit patterns form digital words and can be read by shining a laser beam on the disc surface and detecting the reflected beam. The information storage capacity of a typical DVD, however, is much higher than a CD. Presently available DVDs have a variety of capacities which depend on the technology used to manufacture the discs. Single-layer technologies can be either single or double-sided with capacities of 4.7 gigabytes and 9.4 gigabytes, respectively. Dual layer technologies which use single or double sided capacities that hold approximately 8.5 gigabytes per side are available. This high information storage capacity makes DVDs suitable for storing not only audio information, but also video information and large amounts of computer data as well.
DVD players have many CD player features, such as the ability to play selections in any order desired and the ability to read information from any point on the disc. However, DVDs can store information in several formats. For example, DVDs which are used to store video information, hereinafter called DVD-VIDEO discs, may use various known information compression algorithms, such as MPEG-2 for video compression/decompression. A DVD may also include high fidelity sound data in the form of linear pulse code modulated data streams that have sampled at various rates. Still other DVD versions, hereinafter called DVD-ROM discs, can store digital data for computer use, and the data may also be compressed on these discs.
Although DVD-ROM and DVD-VIDEO discs share compression algorithms, the data format on DVD-VIDEO discs is significantly different than the data format found on DVD-ROM discs. One important difference is that the data content on DVD-ROM is platform-specific, while DVD-VIDEO discs operate with a platform independent navigation engine for playing interactive movies. This navigation engine requires that the files on the DVD-VIDEO disc be referenced in a predetermined directory structure.
The specific navigational commands that are recognized by a DVD player are controlled by a device independent language and a set of DVD player parameters that define the current state of the DVD player. The DVD command set, including the aforementioned commands and their definitions, are published in the DVD specification. A copy of the DVD 1.0 Specification for Read-Only Disc Vol. 3, including a more detailed description of all DVD commands, may be obtained, for example, from Toshiba Corp., 1-1 Shibaura 1-Chome, Minato-ku, Tokyo 105-01 Japan.
In particular, each DVD-VIDEO disc contains a main directory denoted as a VIDEO.sub.-- TS directory that contains two types of files distinguished with the file extensions .IFO and .VOB. During playback, these files are sorted by a DVD video player to form video "title" sets, that are groupings of all files necessary to play a particular DVD video "title", for example, a movie. Each video title set is composed of one IFO file and one or more .VOB files.
A file with the .VOB extension contains the actual multimedia data and is called a video object set. The location and format of the multimedia data stored in the video object set is defined by the associated .IFO file. In particular, .IFO files contain navigational data structures and a processor-independent interpreted language which specifies how the data structures are arranged.
The data structures themselves are composed of various objects called "program chain objects", "program objects", and "cell objects". Program chain objects link related program objects (or particular scenes) within a title and their data structures govern the playback of the program objects. For example, a simple title may contain only one program chain. However, complex titles may contain two or more program chains to allow random access to a variety of programs. The multiple program chain title can play programs linearly, randomly or in a "shuffle" mode. Program chains allow a particular program sequence to be changed during playback. Thus, it is possible to change the program contact based on stored information. This type of operation is used in implementing "parental control" levels in which information content which parents might find inappropriate (such as extremely violent or sexual material) can be removed from a playback and other material substituted without requiring several separate and complete programs.
Each program object in a program chain is composed of elements called "cell objects". These objects instruct a DVD player which portion of the multimedia data in one of the .VOB files to decode. In particular, the data structures in a cell object are defined in the .IFO file and the multimedia content is found in one of the .VOB files. Each cell object directs the DVD player to begin playback at a specific location in the .VOB file which is referred to as a video object unit or "VOBU". A VOBU is a container object that includes both multimedia data and playback program commands. More specifically, each VOBU may contain a header or navigation pack called an "NV.sub.-- PACK" that, in turn, contains navigational commands, user operation data and "highlight" commands which control the presentation of the information on the display.
The specific program commands which are recognized by a DVD player are controlled by a device independent language and a set of DVD player parameters which define the current state of the DVD player. These commands cause the DVD player to perform a number of operations, such as generating menu controls at specific locations on the display screen. In order to process these commands a DVD player system typically includes a processor and associated memory (which may be part of the player or a separate computer) and display device. The player system may be controlled by a playback program running on an operating system such as the WINDOWS NT.RTM., commercially available from MicroSoft Corp., Redmond, Wash., or the OS/2.RTM. operating system, commercially available from IBM Corp., Armonk, N.Y.
Navigational input can also be obtained directly from a user by means of navigational buttons which are displayed on-screen, along with the multimedia data, under playback program control. The playback program controls both the time duration that the button appears on the screen and the manner in which the system responds to the selection of a button by a user. For example, user selection of a button may cause the playback program to jump to a new location on the disc and begin playback at the new location.
The DVD specification for Read-Only Disc Vol 3, enables content to accept user input via on-screen buttons. These buttons are typically rectangular areas, although other shapes are possible, such as square, triangle, round, oval, etc., that allow a user to activate a modification or action by clicking the pointing device while overlaying the button. When a user accesses the navigational commands with a pointing device, such as a mouse, the user manipulates the pointing icon to the desired command or button. Once the user has located the desired command, the user clicks on the button with the pointing device to select or activate the command. The user navigators currently available use linear processing to determine the coordinates of each button. The pointing icon typically falls within a range of coordinates to signify that a given button has been selected.
Buttons are typically displayed within a subpicture area of the video display. That is, a video processor typically combines subpicture information with video information to produce a video output having an "overlay" of subpicture information. Some buttons, referred to as "user buttons", are accessible via a remote control device's numeric keypad entry, other buttons, referred to as "non-user buttons" are accessible via the device's directional arrows, i.e., up, down, left and right.
Pointing devices, such as a mouse, a joystick or a stylus, do not generate directional command data. That is, pointing devices require a user to place a cursor "over" a displayed button, then "click" on the button in order to activate, or select, it. As a result, there is no provision within the DVD specification for such pointing devices to access non-user buttons, i.e., the buttons that are normally accessed by the directional arrows on a remote control device.
Accordingly, a need exists for a technique by which DVD players designed according to legacy specifications can access displayed buttons via a mouse, a stylus or other pointing device while still complying with the specifications to which they were designed.